1. Field of the Invention
The present invention pertains to the field of computer systems. More particularly, this invention relates to a method for managing the power consumption of removable devices in a computer system.
2. Background
Recent portable computer systems such as laptop computers and palmtop computers typically contain resident devices such as a keyboard, a display device, and a disk storage device. Typically, such resident devices are devices embedded within the computer system. In addition, such resident devices may include semipermanent devices or devices not intended for regular installation and removal. Resident devices are typically assembled into a computer system during manufacture of the computer system or are installed during a field system upgrade of the computer system.
In addition, some recent portable computer systems provide standardized card slots for accepting removable devices. Such removable devices are designed for regular insertion and removal from the standardized card slots as needed. Such removable devices may include, for example, flash memory cards, rotating mass storage devices, and fax-modem cards. Typically, such removable devices conform to a standardized form factor for the card slots that accept the removable devices. Such a standardized form factor enables a wide variety of devices to be freely inserted and removed from the standardized card slots in the computer system.
Typically, such a portable computer system includes a battery subsystem that provides power to the system including the resident devices and the removable devices. Such a battery subsystem is typically capable of supplying a limited amount of peak electrical current to the system. The amount of electrical current available from such a battery subsystem is usually determined by a maximum electrical current rating for the battery subsystem.
Prior portable computer systems typically allocate fixed levels of power to each of the standardized card slots that accept removable devices. As the user inserts removable devices into the standardized card slots, the electrical current demands on the battery subsystem increases. As a consequence, the insertion of removable devices may cause the power demands on the battery subsystem to exceed the maximum current rating.
The amount of electrical power available to newly inserted removable devices from such battery subsystem usually varies according to the state of the resident devices and the state of the other removable devices in the standardized card slots. For example, the amount of power available to a newly inserted removable device increases if a resident disk subsystem in the computer system is in a sleep state or power down state.
In addition, differing types of removable devices have differing electrical power requirements. For example, a removable fax-modem card typically consumes more electrical power than a removable static random access memory card.
Moreover, the power consumption of a removable device usually varies according to the functional mode of the removable device. For example, a typical removable flash memory card requires more electrical current during flash program and erase operations than during read operations to the flash memory card. In addition, some prior removable flash memory devices are capable of performing multiple concurrent erase operations. In such devices, the electrical power consumption varies according to the number of flash program or erase operations that overlap in time.
Unfortunately, prior portable computer systems that provide fixed power allocation to standardized card slots cannot efficiently manage electrical power as removable devices are inserted and removed from the system. Such a prior system may indicate that electrical power is not available for a newly inserted removable device even though the power states and operating modes of the other devices provide enough electrical current capacity. As a consequence, the ability of such a prior portable computer systems to adapt to the insertion and removal of removable devices is severely limited. Such a limited power management capability limits the utility and versatility of a portable computer system that provides such standardized card slot mechanisms.